1. Field of the Invention
The present invention relates to means for making improved color corrections.
2. Description of the Prior Art
U.S. Pat. No. 3,848,856 describes an apparatus in which a raster scan scans a color image, for example, a color slide or finished color extraction and supplies a set of color component signals which are subjected to an electronic color correction and then supplied to a video display receiver for observation and control. The color component signals represent the color dosage values for the individual print colors magenta, cyan, yellow and black and are to be corrected with an apparatus having a level indicator under viewing control. So that color images will also be formed on the video receiver, the impression is produced by an image printed with the corrected color component signals with the aid of the corresponding color extractions and a print simulating stage is provided between the correction stage and the video receiver which takes into consideration the fixed parameters of the respective printing process for display. In the color monitor the corrected color picture is displayed in order to control the color correction i.e. the judgement of the correction and the adjusting of the color correction stage. In the published German Patent Application No. 1924309 a method and an apparatus for controlling the mixture of colors during a reproduction process are disclosed, wherein representative gray values of the finished color separations are measured in order to determine the dosage of the color inks during the printing process (page 2, last paragraph and page 3, paragraph 1 of the published German Patent Application). On page 3, paragraph 2 and in claim 1 is further disclosed, that after photoelectrically measuring the corrected color separations, magenta, yellow and cyan the currents of the photocells are fed via amplifiers to electromechanically driven devices for shifting illuminated foil strips bearing color wedge filters representing the full shading range of the separated colors.
These movable wedge filters are arranged beyond a control field which is surrounded by a white environment which has the same white as the white of the foil strips in order to achieve that a small variation of the color value which differs from the environment is recognised.
The environment of the control field can also be colored, but in this case the color should be the same as the color in which the measured picture point of the color separation shall appear after printing.
The method of the published German Patent Application allows the match the density range of the corrected color separations to the density range of the used printing process. The environment of the control field serves to gauge the white level or another color level of the printing process without having an influence of the whole density range of the separations during color correction. In the apparatus according to the U.S. Pat. No. 3,848,856 this procedure is performed by a special print simulating stage which is arranged between the color correction stage and the monitor. This print simulating stage may be programmed e.g. by the parameters obtained by the measuring method of the published German patent application. The problem of my present invention is not to gauge this print simulating stage according to special elected picture points, but to make an improved color correction with respect of the entire impression of the whole picture.